Process and device for grinding a profile of a workpiece

ABSTRACT

On a device for grinding the profile of a rotating workpiece ( 5 ), the rotating workpiece ( 5 ), arranged on a swivel table ( 6 ) for axial and transverse displacement with reference to the work spindle ( 4 ), is according to the invention positioned prior to grinding and relative to a swivel table axis (D) such that the radial centre of a circular arc shaped workpiece profile section ( 7 ) due for high precision grinding coincides with the swivel axis (D) of the swivel table ( 6 ). The thereby attained reduction of the number of simultaneous axes motions involved in grinding this profile section ( 7 ) to a single machine axis permits an optimum profile accuracy.

SUMMARY OF THE INVENTION

One object of the present invention is therefore to introduce a process and a device of the initially stated type, by means of which undesirable profile deviations on the machined workpiece can be reduced.

This object is achieved with a process and a device according to the claims 1 and 8 respectively.

In the process according to the invention and with the device according to the invention for the grinding of an approximately or exactly circular arc shaped profile section of a workpiece on a grinding machine, the workpiece is set up on a work spindle, the work spindle being located on a swivel table swivellable about a swivel axis. The set up workpiece is displaced, together with the work spindle, to a position in which the distance of the radial centre of the profile section relative to the swivel axis of the swivel table is minimized. This profile section is then ground.

The invention exploits the fact that especially at high feedrates and accelerations of the involved motional axes the profile deviations are smallest when as far as possible only a single NC axis must be moved in order to generate a profile section to the prescribed extreme accuracy.

The arrangement of the axes of motion on the machine according to the invention allows the workpiece to be positioned with high precision, such that critical circular arc shaped sections of the workpiece profile can be produced by a swivel action as sole axis motion. The swivel action is generated by means of a swivel table on which the work spindle is located.

If the workpiece profile section to be ground is not an exact circular arc, the distance of an approximate radial centre of the profile section from the swivel axis is minimized; i.e. the position of the workpiece is so adjusted that the accelerations of the remaining machine axes, now inevitably involved in the grinding process, are minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention is explained in detail by way of a preferred embodiment which is illustrated in the annexed drawings. The drawings depict:

FIG. 1 A diagrammatic representation of a tool grinding machine according to the background of the invention,

FIG. 2 A diagrammatic representation of a preferred embodiment of a grinding device according to the invention,

FIG. 3 An enlarged diagrammatic representation of the grinding device according to the invention as shown in FIG. 2, in plan view, and

FIG. 4 An enlarged representation of a detail E indicated in FIG. 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 2 shows diagrammatically a device for grinding the profile of a rotating workpiece 5 in a preferred embodiment according to the invention. This multi-axes numerically controlled grinding machine is composed of a machine column/bed 3, on which a compound slide with two positioning slides 10, 11 is arranged. Attached to this compound slide 10, 11 for rotation about a first horizontal rotary axis B is a grinding spindle 1. The machine bed 3 is furthermore provided with a third positioning slide 14 for a work spindle 4.

The grinding spindle 1 serves to accommodate a grinding tool, in particular a grinding wheel 2 or another tool suitable for the desired machining process. It is located on a machine column 3 for linear displacement in the direction of a first machine axis X and in the direction of a second machine axis Z at right angles to the axis X. As is known from the background of the invention, it can be connected via a swivel head 15 to the compound slide 10, 11. This is not necessary, however, and nor is it the case in this embodiment.

Opposite to the grinding spindle 1 the machine bed 3 is provided with a third positioning slide 14, on which a swivel table 6 is located. The swivel table can thus be displaced in the linear direction of the third machine axis Y. Arranged on the swivel table 6 are two more positioning slides 12, 13 in cross configuration. Located for rotation in the uppermost positioning slide 13 is the work spindle 4 for accommodating a workpiece 5 to be machined. The workpiece 5 rotates about a horizontal axis A which coincides with the longitudinal axis of the work spindle 4.

The compound slide 12, 13 permits a linear displacement of the work spindle 4 along an axial stroke direction U and along a transverse stroke direction V. It is irrelevant which of the two slides 12, 13 is arranged at the top and which at the bottom.

The swivel table 6 permits a swivelling of the compound slide 12, 13, and hence of the work spindle 4 about a swivel axis D. This swivel axis D runs in the vertical direction, i.e. at right angles to the axial and transverse stroke directions U, V, and also at right angles to the work spindle 4.

By swivelling about the swivel axis D and appropriate translatory displacement along the Y, U and V axes, the workpiece 5 can be brought to the grinding wheel 2 and optimally positioned for its subsequent machining.

Referring to FIG. 3, an example of such an optimum positioning is described. For a simple machining example a workpiece 5 is shown, the profile of which contains a profile section 7 of circular arc shape. This profile section 7 is to be ground to the highest accuracy. In order to guarantee this, according to the invention the workpiece is displaced, prior to machining, relative to the swivel axis D in the axes directions U and V to a position at which the radial centre of the circular arc shaped profile section 7 of the workpiece coincides with the swivel axis D of the swivel table 6, as is shown in FIG. 4.

It is thereby achieved that the swivel action of the swivel table 6 alone is adequate for producing the circular arc shaped section 7 of the workpiece profile, and the contour accuracy is not impaired by the superpositioning of the motions of several motion axes, as would be the case if the radial centre of the arc shaped section 7 of the workpiece profile did not lie on the swivel axis D.

If the workpiece 5 contains further circular arc profile sections 8, 9, which must likewise be ground with the highest precision, the grinding process is interrupted after the grinding of the first arc shaped section 7 of the workpiece profile, and not resumed until the radial centre of the next profile section has been exactly positioned on the swivel axis D of the swivel table 6.

If the workpiece profile sections 7, 8, 9 are only approximately of circular arc shape, the position of the workpiece 5 relative to the swivel axis D is selected such that the accelerations of the linear machine axes involved in the profile generation stay as low as possible during grinding. The distance from the radial centre is thus not equal to zero. Instead an approximated radial centre is brought to coincide with the swivel axis.

The device according to the invention increases the accuracy of the profiles by reducing the simultaneous axes motions for grinding this profile to a single machine axis.

List of Reference Numbers

-   1 Grinding spindle -   2 Grinding wheel -   3 Machine column/bed -   4 Work spindle -   5 Workpiece -   6 Swivel table -   7/8/9 Circular arc shaped workpiece profile sections -   10 Fist positioning slide of the grinding spindle -   11 Second positioning slide of the grinding spindle -   12 First positioning slide of the work spindle -   13 Second positioning slide of the work spindle -   14 Positioning slide of the swivel table -   15 Swivel head -   A Axis of rotation of the workpiece -   B Axis of rotation of the grinding wheel -   C Swivel axis of the grinding spindle -   D Swivel axis of the positioning slide of the work spindle -   X Axial stroke direction of the grinding wheel -   Y Infeed direction of the swivel table -   Z Vertical stroke direction of the grinding wheel -   U Axial stroke direction of the work spindle -   V Transverse stroke direction of the work spindle 

1. Process for grinding a profile of a workpiece on a grinding machine, said workpiece having an approximately circular arc shaped or a truly circular arc shaped profile section with a radial centre, said process comprising the steps of: attaching the workpiece to a work spindle, the work spindle being arranged on a swivel table swivellable about a swivel axis, shifting the set up workpiece, together with the work spindle, to a position in which the distance of the radial centre of said profile section relative to the swivel axis of the swivel table is minimized, and grinding said profile section.
 2. Process according to claim 1 wherein, in the case of a truly circular arc shaped profile, the set up workpiece is shifted, together with the work spindle, such that the radial centre of the circular arc shaped profile section comes to lie on the swivel axis of the swivel table.
 3. Process according to claim 1 wherein, in the case of an only approximately circular arc shaped profile section, the position of the workpiece relative to the swivel axis is so selected that an acceleration of machine axes of the grinding machine which are involved in the generation of the profile section during grinding is minimized.
 4. Process according to claim 1, wherein to reach the stated position, the work spindle is shifted in linear manner.
 5. Process according to claim 4, wherein to reach the stated position, the work spindle is additionally swivelled about the swivel axis.
 6. Process according to claim 1, wherein the workpiece is rotated during grinding.
 7. Process according to claim 1, wherein, in the case of a workpiece profile with several approximately circular arc shaped or truly circular arc shaped profile sections, a. the set up workpiece is brought to a first position in which the distance of the radial centre of a first of these profile sections relative to the swivel axis of the swivel table is minimized, and b. this first profile section is subsequently ground, c. the grinding process is interrupted after the grinding of this first workpiece profile section, d. the set up workpiece is shifted, together with the work spindle to a second position, in which the distance of the radial centre of a second of these profile sections relative to the swivel axis of the swivel table is minimized, and e. this second profile section is subsequently ground, and f. the operations c) to e) are repeated so often until all these profile sections have been ground.
 8. Device for grinding a profile of a workpiece by means of a tool, the device comprising a machine column/bed, a grinding spindle connected to the machine column for accommodating the tool, and a work spindle connected to the machine bed for accommodating the workpiece, wherein the device is provided with a swivel table with a swivel axis, the work spindle being arranged on said swivel table for swivelling about the swivel axis.
 9. Device according to claim 8, wherein the work spindle is arranged for linear displacement on the swivel table in at least one direction.
 10. Device according to claim 9, wherein the work spindle is displaceable along two linear axes at right angles to each other.
 11. Device according to claim 8, wherein the swivel table is displaceable along at least one linear axis relative to the machine column/bed.
 12. Device according to claim 9, wherein the swivel axis runs in the vertical direction and the linear displacement of the work spindle takes place in at least one horizontal direction.
 13. Device according to claim 8, wherein a compound slide is arranged on the swivel table, the work spindle being attached to said compound slide. 